This invention relates to a packaging apparatus and a method of forming packages. More specifically, this invention relates to a form fill seal machine in which the longitudinal seam is continuously formed. The cross sealing jaws can be of the type that move downwardly during the sealing operation and are synchronized with the film and the package being formed or of the type that do not move along the direction of the film feed.
The cross seal mechanism that seals the top and bottom of each package produced on a form-fill-seal packaging systems is a critical component of such a system insofar as controlling the quality of the package. The cross seal mechanism must operate at a precise time in the package cycle and must complete its operation with precision and speed.
Reference is hereby made to U.S. Pat. No. 5,715,656 ('656 patent) for a more complete disclosure of the form-fill-seal machine disclosed herein. The subject matter of the '656 patent is hereby incorporated by reference as a part of this application.
The cross seal mechanism disclosed in the above identified '656 patent moves horizontally but does not move vertically. Thus, in that machine, vertical movement of the tubular container must cease during the cross sealing operation and then resume after the cross sealing operation has been completed.
Current cross seal mechanisms are complex and require constant monitoring and adjustment to assure the quality of the finished product. The intermittent or discontinuous movement of the film and the tubular package formed therefrom introduces problems in maintaining control over the film and complicates the film feeding mechanism and its controls. For these and other reasons, there is a need for cross sealing mechanisms that perform the sealing and severing operations while moving vertically in time with the vertical movement of the package being formed.
A form-fill-seal machine in which the cross sealing jaws move downwardly during the sealing operation is disclosed in U.S. Pat. No. 5,752,370 ('370 patent). In this patent, the cross sealing jaws move in the direction of the moving film during the cross sealing operation. The drive for the cross sealing jaws includes a pair of gear cases on opposite sides of the sealing jaws each having two sets of spaced drive shafts. The drive shafts include cranks that impart rotary motion to a pair of link bases for the front and rear sealing jaws. Pairs of parallel links are pivotally connected at one end to the link bases and at the other end to the sealing jaws. The pivot connections of the parallel links include pressure or torsion members which bias the sealing jaws toward engagement. The subject matter of the '370 patent is hereby incorporated by reference as a part of this application.
A form-fill-seal machine is disclosed in U.S. patent application Ser. No. 08/984,812 now U.S. Pat. No. 5,852,920 in which a heated longitudinal seam sealer continuously forms a longitudinal fin seam along the marginal edges of the film. The fin seam is formed by folding the marginal edges of the film outwardly, such that the inner surfaces of both marginal edges engage. Both engaged surfaces are on the same surface of the film. Heat and pressure are simultaneously applied to the outer surfaces of the marginal edges. The outer film surfaces are non-sticky and are generally very tough. Supported films with the sealant run very well on this fin sealer. However, the resulting seam protrudes away from the outer surface of the finished package. Packages that are produced from non-fusible material, for example paper, can be produced using this backseal. When this backsealer is used, one surface of the non-fusible material is coated or laminated with an adhesive or fusible layer that will fuse when heat is applied. This type of seam is most often used for packages, for example breakfast cereal bags, that will be packaged in a carton. This longitudinal seam sealer can be used in machines having conventional cross sealing jaws as well as in machines in which the cross sealing jaws move in the direction of the moving film during the cross sealing operation. The heated longitudinal seam sealer includes a pair of sealer bars that include shaped confronting portions that are heated. The shaped confronting portions function to seal the marginal edges to thus form a fin seam. After exiting the shaped confronting portions, the seam is engaged by a pair of pressure rollers that force the heated marginal edges together to insure complete closure of the fin seam.
Fin type seals are not preferred in plastic bags commonly referred to as pillow bags. The outer surfaces of most pillow bags include printed material describing the contents of the bag and its source. A fin seam protruding from the surface of a pillow bag is folded over. The preferred longitudinal seam for pillow bags, for example a bag of vegetables, is a lap seam. A lap seam is formed by overlapping one marginal edge with a second marginal edge of the film. When this is done on a form-fill-seal machine the engaging surfaces are from opposite surfaces of the film. Thus, to form a lap seam with non fusible material it would be necessary to coat or laminate both surfaces of the film with an adhesive material, which would add unnecessary cost to the product. However, if the film is fusible, for example if the film is a polyethylene material, the opposite surfaces of the film can be fused. However, if the web material is a light polyethylene material then pressure cannot be applied when heating the film. When light polyethylene film is heated to a sufficient temperature to seal the film, the film has nearly zero structural strength. As a result when producing a longitudinal lap seam the seaming mechanism must be essentially friction free so to not produce a drag on the film. Yet to assure a seal having adequate strength the application of some pressure is important. In the preferred embodiment, sufficient pressure is provided by the stream of hot air from the external hot air dispenser. However, in some situations, a very light roller pressure could be utilized.
Thus a longitudinal backsealer, for use with a form-fill-seal machine, is needed that will produce a continuous lap seam that posses adequate strength.